Platable polypropylene

ABSTRACT

Plating grade polypropylene mixture including about 5% to about 7% methyl abietate into the polymer.

United States Patent [191 111 3,926,932 Abu-Isa Dec. 16, 1975 PLATABLE POLYPROPYLENE 58 Field of Search 260/93.7, 94.9 GD [75] Inventor: Ismat A. Abu-Isa, Birmingham,

Mich [56] References Cited [73] Assignee: General Motors Corporation, UNITED STATES PATENTS D i Mi h 3,220,966 11/1965 Flanagan 260/949 GD 3,499,881 3/1970 Poppe et al. 260/949 GD [22] Filed: Jan. 28, 1974 Prima Examiner-Jose h L. Schofer 21 A l. N .1 436,8 1 W P 1 pp 0 8 Assistant Examiner-A. Holler Related Appllcatlon Data Attorney, Agent, or FirmLawrence B. Plant [60] Continuation of Ser. No. 238,464, Nov. 27, 1972,

abandoned, which is a division of Ser. No. 66,127, [57] ABSTRACT 1970 Plating grade polypropylene mixture including about 52 us. or. 260/93.7; 260/949 GD 5% to abut 7% methyl abetate the polymer- [51] Int. Cl. C08f 29/02 1 Claim, N0 Drawings- PLATABLE POLYPROPYLENE This application is a continuation of application Ser. No. 238,464, filed Nov. 27, 1972, now abandoned, which in turn is a divisional of application Ser. No. 66,127, filed Aug. 21, 1970, now US. Pat. No.

This invention relates to the metal plating of polypropylene compositions. In the beginning, injection molded polypropylene articles were difficult to metal plate uniformly. Commercially available grades of polypropylene would not etch uniformly without a preetch treatment which involved soaking the polymer in an organic swelling agent, such as turpentine or the like. More recently, polypropylene compositions have been developed and marketed which do not require organic pre-etch treatments. These later compositions contain additives which promote uniform etching/oxidizing of the polypropylene composition. This, in turn, enhances the ability of the polypropylene to accept a uniform electroless deposit of metal. While certain of these addition agents do improve the platability of polypropylene, their presence apparently causes the polypropylene to suffer a loss with' respect to some of its other properties, notably impact strength and hea deflection resistance.

Accordingly it is an object of this invention to provide a plating improver which is mixed with and absorbed by the propylene to produce a readily platable composition which has improved processing characteristics, impact strength, heat deflection resistance and adhesion values. This and other objects of this invention will become more apparent from the detailed description which follows.

In accordance with this invention methyl abietate is absorbed into at least the surface, but preferably all, of the part to be plated such that the concentration of the methyl abietate is at least about 2% by weight, of the mixture of methyl abietate and polypropylene at the surface to be plated. Methyl abietate concentrations of about 5 to 7% throughout the polypropylene are preferred. In these latter concentrations the physical properties of the polypropylene are significantly improved and the etching time minimized. No appreciable benefits are derived from methyl abietate concentrations in excess of about by weight. The higher methyl abietate concentrations consume excessive amounts of oxidant (i.e., CrO during the surface oxidation etching step and returns no significant benefit over the use of the preferred 5 7%.

As used herein, the term polypropylene is intended to include both the polypropylene homopolymers and the principal copolymers thereof, such as the ethylenepropylene copolymers. Likewise, as used herein, the term methyl abietate is intended to include the methyl esters of the resin acids found in rosin. A mixture of such acids is commercially available under the name Abalyn. In this latter regard, The Condensed Chemical Dictionary, 6th Ed., Arthur and Rose, advises that the term abietic acid relates to the major active ingredient of rosin and is often applied to mixtures of acids which have closely related structure and proper- V least two ways. In the preferred form, the methyl abiet-' ate is mixed uniformly with all of the polypropylene before it is injection molded into a given article. In this regard, a measured amount of methyl abietate, which is a viscous liquid, is added to a measured amount of polypropylene flakes and mixed in a Hinchel blender until the flakes completely absorb the methyl abietate and again become free-flowing. Injection molded articles made from polypropylene compositions thusly prepared, in addition to being more uniformly platable, have demonstrated higher impact strengths, better heat deflection characteristics and are less stressed in the as-molded condition than comparable articles prepared without the methyl abietate addition. Additionally, the methyl abietate treated polypropylene is more easily processed, especially during mixing operations such as during the blending of fillers with the polypropylene.

In another embodiment, the methyl abietate is absorbed into the surface of an article which has first been formed (e.g., injection molded) from a conventional non-plating grade polypropylene (e.g., Hercules 6523). This is accomplished by soaking the article in a suspension of methyl abietate (e.g., about 10%) in water, plus a non-ionic detergent (e.g., FC-95 anionic fluoro-chemical by Minnesota Mining & Manufacturing) to wet the polypropylene. Soaking continues until the surface absorbs a sufficient amount of the methyl abietate to provide at least the aforesaid minimum 2% concentration of the methyl abietate at the surface.

When the concentration of methyl abietate falls below about 2%, it is not practically possible to consistently uniformly etch or oxidize the surface within a reasonable amount of time, i.e., less than about 20 minutes. Uniform oxidation of the surface is required to obtain a uniformly deposited, strongly adherent electroless metal coating. On the other hand, when the concentration of methyl abietate exceeds about 15%, the polypropylene begins to feel oily to the touch resulting from the apparent saturation of the polypropylene with the methyl abietate. In this oily condition the methyl abietate provides no significant benefits over the lower and preferred concentrations and in fact is detrimental to the extent that it non-usefully consumes an excess amount of oxidant from the etching/oxidizing solution.

In a preferred embodiment of this invention, the methyl abietate is mixed completely throughout the polypropylene mixture and tends to plasticize it. It is this embodiment which yields the most significant improvements in the physical properties (i.e., impact strength, heat deflection, etc.) of the finished molded part itself, as-distinguished from simply its platability. In this regard and in order to still further improve the properties and reduce the costs of the molded parts made from polypropylene mixtures of this invention, any of the conventional fillers (e.g., talc, titanium dioxide, etc.) typically used with thermoplastics may be used. When used, the fillers may comprise as little as 2% to as much as 50% of the finished injected molded article, though it is preferred here to use about 3 8% filler content.

Polypropylene mixtures prepared in accordance with this invention are platable using any of the conventional polymer plating processes known to those skilled in the art. Such conventional processes usually involve etching the surface with a strong oxidizing agent, sensitizing it with an aqueous SnCl solution, activating it with a PdClg solution and then electrolessly depositing a metal (e.g., Ni) onto the surface followed by any desired electroplating sequence. Likewise, polypropyl- 3 able MaCuplex system marketed by MacDermid, Inc. That process is a variation of that described above and involves the use of a mixture of stannous chloride and colloidal palladium instead of the more conventional 4 tion containing about 36 grams per liter nickel sulfate heptahydrate, 3.6 grams per liter sodium hydroxide, 28 grams per liter sodium hypophosphite, 13 cc per liter acetic acid and drops of lead concentrate (1 g/l sensitizing solution. This step is followed by a palla- 5 Pb). The pieceswere rinsed and next electroplated dium chloride accelerator treatment. Likewise, the with 2 mils of conventional acid copper (sulfate type) polypropylenes of this invention may be used in sys and then aged for at least 72 hours. Several of the terns employing organic swelling pre-etch treatments, pieces were then adhesion tested according to the J acthough as indicated before, such treatments are not quet test described in the article by E. B. Saubestre, J. necessary with methyl abietate treated polypropylenes. l0 Durney, G. Hajdow, E. Bastenbach, Plating, 52, 983, In the etching, or surface oxidizing step, it is pre- 1965. This test involves scribing a one (1) inch strip ferred to use the strongest oxidizing solutions possible. oss and through the copper and nickel layers, lifting Aqueous solutions containing at least about 800 grams a tab at the end of the strip, grasping the tab in an Inper liter of CrO are most preferred, but the more con- St on mac ne, Pu ng rip at a rate of One inch ventional H 80 CrO etching systems may also be per minute at an angle of 90 from the face of the panel, used. Such solutions insure uniform oxidation of the and recording the amount of pull (i.e., lbs./in.) resurface in the shortest possible time. quired to peel the strip from the panel. The remaining A number of tests have been conducted and their depieces were processed in the following manner. A 0.7 scription will serve as specific examples of this invenmil layer of semi-bright nickel (Udylite N Covered tion. In these tests, a number of pieces were injection the ac d Copper. This was followed by a 0.4 mil layer of molded from mixtures containing polypropylene flakes bright nickel (Udylite 66) and finally by a 0.01 mil (Hercules 6523), methyl abietate (Abalyn) and filler layer of chromium. The thusly plated pieces were aged (tale). The methyl abietate and polypropylene were for at least 72 hours and then subjected to thermal cyfirst mixed for about 10 minutes in a Hinchel blender at cling in accordance with the following sequence which about 500 rpm until the methyl abietate was uniformly as repeated for four cycles one hour at 185F., l5 absorbed into the polypropylene flakes, This mixture minutes at 72F., one hour at 20F., and 15 minutes at was then placed in a screw fed injection molding ma- 72F. chine with a measured amount of talc, thoroughly The following tables reflect typical results of pieces mixed and melted. The melt was injected into a mold at este in ccordance with the procedure described about 230F. and 800 psi pressure. After cooling, the above. In Table I all samples except number 6, were pieces were removed and aged for about 24 hours. Sevcompounded using polypropylene flakes identified as era] of these pieces were then impact strength tested H r ules 6523- Sa ple 6 is the data ep y using the Notched Izod test described in ASTM D 256, Avison Co. for their plating grade polypropylene (TD heat deflection tested during the test described in 270A). ASTM D 648, d h d tested using h test d While this invention has been described in terms of scribed in ASTM D 785. The remaining pieces wer specific embodiments thereof it is not intended that it Table I Percent Impact Str. Heat Deflection Rockwell Adhesion Sample Methyl ASTM D 256 ASTM D 648 Hardness Jacquet Test Abietate Filler (ft.-lbs.) (66 psi) ASTM D 785 (Lbs/in.)

1 0 0 0.65 102C. 830 2 6% 0 1.27 540 20 3 3% 3% Tio 1.15 4 6% 5% talc 1.07 105C. 35 5 5% 3% talc 1.24 6 0.38 94 800 18-24 Table II Percent Adhesion Sample Methyl Etch Time Post-Etch Jacquet Test Thermal Abietate Filler (Min) Appearance (lbs/in.) Cycling l 2% 0 20 (90C.) good Passed tape test 2 5% 0 5 (90C.) good lS-20 Passed 3 6% 0 7 (85C.) good 18-20 Passed 4 6% 5% talc 5 (80C.) good 35-50 Passed 5 15% 0 5 (80C.) oily Passed tape test processed as follows. The pieces were immersed in a be limited thereto, except to the extent hereinafter set 75C. chromic acid etching solution containing 900 0 th in the appended claim which follows. grams per liter of CrO After rinsing, the pieces were I'claim; treated for 3 minutes in a room temperature, acidic, 1. Plating grade polypropylenev flakes for forming aqueous stannous chloride solution containing about into rigid articles destined to be metal plated, said 35 grams per liter of SnCl and 30 milliliters per liter of flakes comprising principally high molecular weight HCl to sensitize its surface. After rinsing, the pieces polypropylene and methyl abietate in which the methyl were next activated for 3 minutes, in a 75F. aqueous, abietate Comprises about 5 to about 7% by weight of palladium chloride solution containing 0.26 gram per liter palladium chloride and 4.5 milliliters per liter HCI. After rinsing, nickel was electrolessly deposited onto the surface for 7 minutes from an aqueous, C. soluthe combined polypropylene and methyl abietate, said high molecular weight polypropylene having a heat deflection of at least about 94C. under a 66 psi load test according to ASTM standard (ASTM D648).

UNITED STATES PATENT AND TRADEMARK OFFICE @ETFFIQATE OF CORRECTION PATENT NO. I 3,926,932

DATED 3 December 16, 1975 INVENTOR(S) I Ismat A. Abu-Isa it is certified that error appears in the ab0veidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 29, the word "propylene" should read polypropylene Column 3, line 34, the word "during" should read using Signed and Scaled this eighteenth Day of Mayl976 [SEAL] Arrest:

RUTH C. MASON 'C. MARSHALL DANN 8 J fifl'r Commissioner nj'l'alems and Trademarks 

1. PLATING GRADE POLYPROPYLENE FLAKES FOR FORMING INTO RIGID ARTICLES DESTINED TO BE METAL PLATED, SAID FLAKES COMPRISING PRINCIPALLY HIGH MOLECULAR WEIGHT POLYPROPYLENE AND METHYL ABIETATE IN WHICH THE METHYL ABIETATE COMPRISES ABOUT 5 TO ABOUT 7% BY WEIGHT OF THE COMBINED POLYPROPYLENE AND METHYL ABIETATE, SAID HIGH MOLECULAR WEIGHT POLYPROPYLENE HAVING A HEAT DEFLECTION OF AT LEAST ABOUT 94*C. UNDER A 66 PSI LOAD TEST ACCORDING TO ASTM STANDARD (ASTM D648). 